(function (window) {
  'use strict';

  function pad(hash, len) {
    while (hash.length < len) {
      hash = '0' + hash;
    }
    return hash;
  }

  function fold(hash, text) {
    var i;
    var chr;
    var len;
    if (text.length === 0) {
      return hash;
    }
    for (i = 0, len = text.length; i < len; i++) {
      chr = text.charCodeAt(i);
      hash = ((hash << 5) - hash) + chr;
      hash |= 0;
    }
    return hash < 0 ? hash * -2 : hash;
  }

  function foldObject(hash, o, seen) {
    return Object.keys(o).sort().reduce(foldKey, hash);
    function foldKey(hash, key) {
      return foldValue(hash, o[key], key, seen);
    }
  }

  function foldValue(input, value, key, seen) {
    var hash = fold(fold(fold(input, key), toString(value)), typeof value);
    if (value === null) {
      return fold(hash, 'null');
    }
    if (value === undefined) {
      return fold(hash, 'undefined');
    }
    if (typeof value === 'object' || typeof value === 'function') {
      if (seen.indexOf(value) !== -1) {
        return fold(hash, '[Circular]' + key);
      }
      seen.push(value);

      var objHash = foldObject(hash, value, seen)

      if (!('valueOf' in value) || typeof value.valueOf !== 'function') {
        return objHash;
      }

      try {
        return fold(objHash, String(value.valueOf()))
      } catch (err) {
        return fold(objHash, '[valueOf exception]' + (err.stack || err.message))
      }
    }
    return fold(hash, value.toString());
  }

  function toString(o) {
    return Object.prototype.toString.call(o);
  }

  function sum(o) {
    return pad(foldValue(0, o, '', []).toString(16), 8);
  }

  window.hash = {
    sum
  };
})(window)
